Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and the like. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources.
A wireless communication network may include a number of base stations that can support communication for a number of mobile devices. In some technologies, mobile devices may be called access terminals, user equipments (UEs), mobile stations, and the like. A mobile device may communicate with a base station via downlink (DL) and uplink (UL) transmissions. The downlink (or forward link) refers to the communication link from the base station to the mobile device, and the uplink (or reverse link) refers to the communication link from the mobile device to the base station.
Multiple access technologies may use Frequency Division Duplexing (FDD) or Time Division Duplexing (TDD) to provide uplink and downlink communications over one or more carriers. TDD operation offers flexible deployments without requiring paired spectrum resources. TDD formats include transmission of frames of data, each including a number of different subframes in which different subframes may be uplink or downlink subframes. In systems that operate using TDD, different formats may be used in which uplink and downlink communications may be asymmetric. Flexible TDD DL/UL configuration provides efficient ways to use unpaired spectrum resources and TDD configuration may be adaptive based on traffic conditions (e.g., UL/DL loading at the base station and/or UE).
The wireless communication networks including the base stations and UEs may support operation on multiple carriers which may be called carrier aggregation. Carrier aggregation may be used to increase throughput between a base station supporting multiple component carriers and a UE, and UEs may be configured to communicate using multiple component carriers associated with multiple base stations. In some instances, carrier aggregation involving both FDD and TDD frame structures may be supported.